Vancomycin is already used for decades in neonates. However, there are remaining questions concerning vancomycin disposition in this population. The purpose of this study is first of all to perform a paired analysis of serum vancomycin concentrations using an immunoassay versus a reference liquid chromatography-tandem mass spectrometry method. Secondly, we aim to determine vancomycin protein binding and its covariates in neonates.